Table of contents

1. Matter and Measurements4h 31m
2. Atoms and the Periodic Table5h 23m
3. Ionic Compounds2h 18m
4. Molecular Compounds2h 18m
5. Classification & Balancing of Chemical Reactions3h 17m
6. Chemical Reactions & Quantities2h 27m
7. Energy, Rate and Equilibrium3h 46m
8. Gases, Liquids and Solids3h 25m
9. Solutions4h 10m
10. Acids and Bases3h 29m
11. Nuclear Chemistry56m
BONUS: Lab Techniques and Procedures1h 38m
BONUS: Mathematical Operations and Functions47m
12. Introduction to Organic Chemistry1h 34m
13. Alkenes, Alkynes, and Aromatic Compounds2h 12m
14. Compounds with Oxygen or Sulfur1h 6m
15. Aldehydes and Ketones1h 1m
16. Carboxylic Acids and Their Derivatives1h 11m
17. Amines39m
18. Amino Acids and Proteins1h 51m
19. Enzymes1h 37m
20. Carbohydrates1h 41m
21. The Generation of Biochemical Energy2h 8m
22. Carbohydrate Metabolism2h 22m
23. Lipids2h 26m
24. Lipid Metabolism1h 45m
25. Protein and Amino Acid Metabolism1h 37m
26. Nucleic Acids and Protein Synthesis2h 54m

18. Amino Acids and Proteins

Amino Acid Classifications

GOB Chemistry

18. Amino Acids and Proteins

Amino Acid Classifications

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Problem 45a

Textbook Question

Name and draw the structures of the amino acids that fit the following descriptions:
a. Contains an isopropyl group

Verified step by step guidance

Step 1: Recall that amino acids are organic compounds containing both an amino group (-NH₂) and a carboxyl group (-COOH), along with a unique side chain (R group) that determines their identity.

Step 2: Identify the amino acid that contains an isopropyl group in its side chain. An isopropyl group is a branched alkyl group with the structure -CH(CH₃)₂.

Step 3: The amino acid with an isopropyl group in its side chain is **valine**. Its side chain is -CH(CH₃)₂, making it a nonpolar, hydrophobic amino acid.

Step 4: Draw the structure of valine. The general structure of an amino acid is: H₂N-CH(R)-COOH, where R is the side chain. For valine, R = -CH(CH₃)₂. The full structure is: H₂N-CH(-CH(CH₃)₂)-COOH.

Step 5: Label the functional groups in the structure. Highlight the amino group (-NH₂), the carboxyl group (-COOH), and the isopropyl side chain (-CH(CH₃)₂) to ensure clarity in the representation of valine.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Amino Acid Structure

Amino acids are organic compounds that serve as the building blocks of proteins. Each amino acid has a central carbon atom (the alpha carbon) bonded to an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom, and a variable side chain (R group) that determines the specific properties of the amino acid. Understanding the general structure of amino acids is essential for identifying specific ones based on their side chains.

Isopropyl Group

The isopropyl group is a branched alkyl group derived from propane, consisting of three carbon atoms with the structure -CH(CH3)2. In the context of amino acids, the presence of an isopropyl group in the side chain indicates that the amino acid has a hydrophobic character, influencing its interactions and positioning within proteins. Recognizing this group is crucial for identifying the correct amino acid.

Hydrophobic Interactions

Hydrophobic interactions refer to the tendency of nonpolar substances to aggregate in aqueous solutions to minimize their exposure to water. Amino acids with hydrophobic side chains, such as those containing isopropyl groups, play a significant role in protein folding and stability. Understanding these interactions helps in predicting how amino acids will behave in a protein's three-dimensional structure.

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Textbook Question

Isoleucine has the zwitterion structure shown. Draw the structure and give the net charge of isoleucine that will predominate at the indicated pH values (pI = 6.0).

b. pH 6.0

695

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Textbook Question

Glycine has the zwitterion structure shown. Draw the structure and give the net charge of glycine that will predominate at the indicated pH values (pI = 6.0).

b. pH 12.0

512

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Textbook Question

Consult Table 18.3 and draw alanine. Label the functional groups and give the three-letter abbreviation and the one-letter abbreviation. What group does the side chain fall into?

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Draw the structure of glutamic acid at low pH, at high pH, and at the two forms that exist between low pH and high pH. Which of these structures represents the zwitterion?

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Textbook Question

Name and draw the structures of the amino acids that fit the following descriptions:

a. Contains a thiol group

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Textbook Question

At neutral pH, which of the following amino acids has a net positive charge, which has a net negative charge, and which is neutral? (Hint: Draw the various charged forms of each amino acid before deciding.)

a. Asparagine

b. Lysine

c. Proline

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Textbook Question

Which of the following forms of aspartic acid would you expect to predominate at low pH, neutral pH, and high pH?

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Textbook Question

Which form of aspartic acid in Problem 18.54 is the zwitterion? What is the pI for the zwitterion?

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